Sweet Corn IPM Newsletter No. 12 — August 29, 2024

CORN PEST PRESSURE LOWER

Cool Night Temperatures Reduce Earworm Activity

SITUATION

Cool nights and favorable weather patterns have reduced pest pressure in most locations this week. Corn earworm numbers were mostly lower but fall armyworm numbers were higher at some sites, posing a risk to all remaining corn in silk. Harvest for the holiday weekend looks good with adequate supply and good quality readily available.

European corn borer: Moths were only found at sites in Bowdoinham and Dayton, where a small second generation of corn borer has been starting. Only the Dayton site was over the spray threshold for moths in silking corn. Very little larval feeding damage was found in pre-silking corn, and no sites were over threshold.

Corn earworm: Cooler night temperatures and stable weather patterns have kept earworm moth activity fairly low this week. Several sites no longer have corn in the fresh silk stage, so earworm is no longer a threat. Once the silks have dried, earworm moths will not typically lay eggs on them. A 6-day spray interval for silking corn was recommended in Auburn, Corinth, Oxford and one Wells site; a 5-day spray interval was recommended in Biddeford, Bowdoinham, Gray and Wayne; a 4-day spray interval was recommended for Cape Elizabeth and Dayton.

Fall armyworm: Moth counts in pheromone traps continue to be variable, but mostly higher this week. Biddeford, Bowdoinham, Cape Elizabeth, Dayton, Gray, Monmouth, and one site in Wells were over the three-moth threshold for silking corn in pheromone traps, but all of these sites except Monmouth are presently under a spray interval for corn earworm, which should provide control of fall armyworm. Larval feeding damage was very light in most pre-silking corn, and most sites have no pre-silking corn remaining. Only the site in Gray was over threshold of 12-15% of plants with fresh injury.

Western Bean Cutworm: No moths were caught in any of our pheromone traps this week.

When Should I Stop Spraying? When a silking corn field is under a recommended spray interval for corn earworm, we recommend that spraying be stopped once the silks have become thoroughly dried and brown. At this stage, corn earworm moths are unlikely to lay eggs on it. However, if earworm pressure is very high (e.g. 91+ moths per week) and/or fall armyworm moths are over threshold (3 or more moths per week), then spraying should continue until either the moth counts drop, or you reach the required days before harvest (dh) for the product being used.

Birds, etc: Flocking species of blackbirds are starting to cause damage in cornfields around the state. They are especially attracted to fields where corn has been allowed to get over-mature. Deer, skunks and raccoons have also been troublesome this year. For information on wildlife problems and management options, you may call the Animal and Plant Health Inspection Service (APHIS) office in Augusta at 1-866-487-3297.

Save the Date!

The New England Vegetable & Fruit Conference will be held in Manchester, NH December 17, 18, 19, 2024. Program and registration information will be coming soon. Visit the website: http://www.newenglandvfc.org/

 

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259
207.933.2100

UMaine Extension Diagnostic Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm
CBW: Western bean cutworm

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer Thresholds

Whorl stage: 30% or more of plants scouted show injury.
Pre-tassel-silk: 15% or more of plants scouted show injury.
Silk: 5 or more moths caught in pheromone traps in one week.

IPM Web Pages:

Explore Integrated Pest Management in Maine — UMaine

Integrated Pest Management Data Visualization Tool — Penn State

Integrated Pest Management — UMass Amherst

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

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